1. Field of the Invention
The present invention relates to an electronic medium with an integrated circuit (IC), such as an RFID tag, which receives a supply of power from an external device, and also relates to a system of operating an electronic medium with IC.
2. Description of the Related Art
An RFID tag that receives a supply of power from a reader/writer device in a non-contact manner and communicates with the reader/writer device using the power has been used widely. Further, an electronic medium having additional values utilizing characteristics of the RFID tag, such as electronic paper as disclosed in Japanese Unexamined Patent Application Publication No. 2009-136556, has also been used widely.
Such an electronic medium has a configuration including an antenna coil and an IC chip that are included in an RFID tag, and a functional unit (electronic paper) as an additional portion, as disclosed in Japanese Unexamined Patent Application Publication No. 2009-136556. The IC chip includes a power feeding system circuit such as a rectifying circuit and a control unit. Further, the existing functional unit receives a control signal from the control unit of the IC chip so as to operate and receive a supply of power from the control unit.
However, as disclosed in the above-described Japanese Unexamined Patent Application Publication No. 2009-136556, when power is supplied from the control unit of the IC chip to the functional unit, power that can be supplied to the functional unit is restricted by a withstand voltage of the control unit.
FIG. 1 is a graph illustrating an example of a relationship between transmitted power that is output from a reader/writer device and power that is actually supplied to a control unit of an IC chip of an RFID tag.
In general, in the RFID tag, a protecting circuit is connected between a rectifying circuit and a smoothing circuit, and a control unit. The rectifying circuit and the smoothing circuit are circuits for obtaining a DC signal for a power source from an AC signal generated on an antenna coil. Further, a voltage to be applied to the control unit is restricted by the protecting circuit so as to prevent the control unit from being broken. Therefore, power to be supplied to the control unit is restricted and supply of power to the control unit is increased only up to power that follows a specification of the protecting circuit even if transmitted power from the reader/writer device is increased, as illustrated in FIG. 1.
Accordingly, the functional unit that receives power from the control unit receives a supply of power of equal to or lower than the restricted power only. Therefore, when a functional unit that cannot be operated with power supplied from the control unit or a functional unit that cannot be continuously operated therewith is added to an electronic medium including an RFID, a power supply source dedicated to the functional unit needs to be added. However, if such a dedicated power supply source is added, problems occur in that a size and shape of the electronic medium is increased more than acceptable, the number of component parts and manufacturing complexity are increased, the cost is increased, and so on.